There is need for rapid, accurate and quantitative or qualitative determinations of substances in biological fluids and for compounds, particularly toxins and contaminants, in the environment and in food. For example, the presence of certain compounds, such as drugs, hormones, peptides, proteins and infectious organisms in blood, urine, saliva, vaginal secretions, dental plaque, cerebral spinal fluid and other biological and environmental samples has to be determined accurately and rapidly.
To provide such determinations, various assays have been developed by which biological and environmental substances can be detected and/or quantified and, if necessary, isolated. Such methods typically rely on specific binding reactions between the substance of interest and a compound specifically reactive with that substance. The resulting reaction or complex is measured or detected by a variety of known methods. The most commonly used methods employ a signal amplifying reagent or moiety of some type that is either already attached to one of the components of the complex, becomes part of the complex through further reaction or reacts with the complex to produce a detectable product. For example, nucleic acid probes may be labeled with biotin, which then binds to avidin or strepavidin. The biotin or avidin/strepavidin are labeled with reporter enzymes or radiolabels. Proteins are often detected with antibodies, which are labeled with reporter molecules, such as enzymes or radiolabels. The resulting complexes are measured by detecting the reporter molecule. Enzyme labels, such as alkaline phosphatase, are advantageous because of their relative stability, signal amplification, and because the labels are non-isotopic, the hazards and difficulties associated with handling and disposing radioisotopes are avoided. In diagnostic tests designed to be rapid and easy to use with moderate training in a doctor's office, clinic or environmental laboratory, the reporter molecule is often detected using colorimetric, fluorescent or chemiluminescent signals resulting from reaction of the enzyme label with its substrate.